This invention is generally directed toward a method of eliminating hysteresis in a magnetoelastic torque sensor. More particularly, this invention is a method of removing remanent magnetism outside of a desired magnetic flux path.
A magnetoelastic torque sensor utilizes one or more bands of magnetoelastic material supported on a substrate. The magnetoelastic bands possess circumferential remanent magnetization bound by the magnetocrystalline anisotropy of the material. Torque applied to the substrate induces a helical shear stress on the magnetoelastic material that results in a shift of the path of the magnetic field from a circumferential to helical orientation. Axial components of the magnetic field are measured utilizing a magnet field measurement device and are utilized to determine torque.
Disadvantageously, once the application of torque on the substrate is discontinued, a remanent portion of the magnetic field remains. The axially-directed remanent magnetic field within the magnetoelastic band causes a shift in a zero point of the torque sensor. The shift of the zero value is commonly known as hysteresis. A known method of eliminating the magnetism within a magnetized body includes placing the structure within an alternating magnetic field with peak amplitude exceeding the coercive force of the material. However, such methods require separate devices that are not available during operation, and remove all magnetic components, even those in the desired circumferential magnetic orientation.
Accordingly, it is desirable to develop a method and device for selectively removing axial hysteretic magnetic remanents, while leaving the desirable circumferential magnetic remanences intact.